Trailing 12 months from specific date interval

Hi Experts!

I need help creating a Measure that is calculating the sum of the last 12 months 'sales'. The problem is that in the same Matrix there is a measure that is showing the sum of sales bassed on a slicer. 

So i need the measure to take the Max date from the slicer but the measure need to go eaerliere then the slicer. so no matter the range of my slicer, the Measure is allways going to show the last 12 months from the max date from the slicer.

This is what i need the end product to look like

The following picture shows that the 'Sales' is the total sales for November but the 'Last 12 months' still shows the total sales for the last 12 months from the max date of the filter.

So the numbers would be:

Sales: Total sales November 2018

last 12 months: Total sales from November 2017 - November 2018

The data model is build as followed 

Fact_Sales

Dim_Date

Dim_Product

As much as i know i need to create another Date dimention and have it disconnected from the rest of the datamodel but i can't figure out how i have to create the measure